Fireheart
by K. Fang-sama
Summary: In the midst of a strange 'illness,' Ulquiorra finds himself on a journey in search for his chosen. What happens when this bat comes face-to-face with a phoenix? KaixUlquiorra. Warning: yaoi, future sex scenes, gore, some OOCness and maybe mpreg.
1. Illness?

_**Well, this ought to be fun. I found it strange that no one wrote a crossover with one of the arrancar as a main character. Then this idea popped into my head. I hope you enjoy it!**_

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**Fireheart**  
**Chapter One:**  
**Illness?**

_Lips met against bare flesh as a set of hands began to remove more clothing that kept the shadowed figure clothed. The person moaned as pale hands roamed his skin; pleasure coursing through the person's veins as the latter continued._

_Green eyes meeting clouded ones, the pale figure asked: "Do you want me?'_

_The person shuddered under him. "Yes," he said through shaky breath._

Bright emerald eyes shot open as their owner jolted upright in his bed. Here, Ulquiorra Cifer-the Cuatro Espada-sat in green sleeping attire; body beading down cold sweat as the porcelain-skinned arrancar tried to catch his breath and get rid of the strange warmth that rose to his cheeks.

"Why do I keep having these strange dreams?" He asked himself, looking at the digital clock on his bedside table. 3:17 am. He sighed once; this was getting annoying. The Espada had only begun having these dreams three nights ago, and so far, he'd already become an insomniac, he had begun hallucinating during the day, he had become more irritable than he remembered being, and finally...

Ulquiorra's eyes widened, now a bit more awake, before looking underneath his bed covers; finding a grotesque smell reaching his nostrils through a warm, rather muggy air. _"Soiled again,"_ he thought; a hand to his head as he dropped the comforter. This was the most embarrassing part of all of this.

With an annoyed glare settle onto his face, Ulquiorra got out of bed, removed his bed linens, and went down the stairs to his laundry room. He never knew how thankful he was for the Espada Houses until this all started; no one got to see anything beyond what he wanted them to see outside his door, and he had full privacy here. If another arrancar were to see what he was doing, his reputation would be in shambles.

He put his black linens in the washer before removing his clothes, placing them in machine, and getting the soap in so he could start the laundry _"Again."_ He reminded himself before grabbing one of the towels he had neatly folded yesterday afternoon and wrapping it around his waist and moving up to the bathroom.

As Ulquiorra cleansed himself under the running shower, he couldn't help but wonder why and how this had all started. He never went through the scenarios of the days before this started but found nothing relevant. At least, nothing he could think of; and even with little sleep, Ulquiorra was still one of the most analytical arrancar there were next to Szayel.

He sighed once more; wanting nothing more than to have this problem solved. The green-eyed male couldn't even think of a time that he had felt so confused, all he knew was that he was ill or something. Yes, ill seemed fitting. He had never experienced these symptoms before, so he was certain they could be treated. All it would take is a trip to see the pink-haired scientist and then he'd be done with this craziness. Now, all he had to do was wait for the scientist to wake up.

* * *

Szayel Aporro Granz woke up at six in the morning, got ready for his day, ate breakfast, and made it to his lab by seven-thirty exact. Just as he always did. He had been preparing his work station for not even five minutes when the telecom rung through his lab.

_"Strange,"_ he thought. No one, not even Tousen himself, was awake at this hour of day, and the blind commander was always up by nine. So, who was up early enough to be bothering him? Grimmjow and Nnoitora slept till early afternoon, so they were out of the question. Zommari would meditate before doing anything, and the earliest he's ever gotten up was eight. Starrk slept till whenever Lilynette forced him out of bed, Harribel slept till about the same time as Tousen and Barragan was too cranky in the morning to do much of anything, let alone bear people his words. Aizen and Gin were only up early on personal matters, so who was left?...

Szayel's head snapped, a smirk on his face when he saw his assumption correct. _Only Ulquiorra could beat him out of bed. _"Ohayou gosaimaizu, Ulquiorra-san." He greeted just after he pressed the answer button.

"Szayel, I need to speak to you in person." He heard the shorter arrancar tell him; his voice distinctly lower than he remembered it being.

His brow perked, a blank expression on his face. "Are you alright, Ulquiorra-san?" He asked his superior.

"No," was the immediate response, the emotionless arrancar's voice sounding alarmingly annoyed. Szayel wisely remained quiet as he heard his superior sigh in an attempt to calm himself. "I believe I've recently grown ill and I need you to take care of it." He was told, more calmly.

The pink-head smiled. _Oh, how he loved his job._ "Very well then. I'll be with you in about ten minutes." He said. And like that, the Cuatro hung up.

Szayel finished prepping his lab before heading to pick up his examination equipment. As he collected it all, he could only help but wonder what it was Ulquiorra had. "Hopefully something interesting." He chimed in his head before leaving for the Cuatro's House.

* * *

Morning came upon Russia; the sun barely visible within the clouded winter sky. Here, sitting in a snow-covered park was the Captain of the Blade Breakers: Kai Hiwatari. The ruby-eyed male sat bundled up from the early winter cold in a long, black winter coat, and was spending his time writing in a red journal.

He didn't know why, but for the past few days he had been waking up earlier than usual, and his focus on his auto-biography of the Abbey was shifted to something else. It was some sappy romance, that he hadn't known he was capable of writing. Yet, here he was; writing away to his heart's content.

The teen didn't know what to make of his creation so far. He had wrote it with the idea of a boy born of phoenix blood stuck in some frosted world, longing for a place of warmth and longing for someone to care about him outside the ring that surrounded him. Kai, for what he figured, might have based the main character off the idea that his bit beast considered him her son, but he wasn't sure. All he knew was that the story was making itself so far.

Closing the book with no title, Kai looked up at the sky that seemed ready to start blowing snow at him again with a solemn look on his face. There didn't seem to be a storm gathering in the sky; allowing him to feel his life was starting to calm for a change...

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_**Good? Bad? Hope it's good. See ya soon!**_

_**~ K. Fang-sama**_


	2. Pressing Matters

_**Okay, chapter two, here we come!**_

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**Chapter Two;**  
**Pressing Matters**

The time was 11:33 am when the results from Szayel's test came back; printing onto a piece of paper from a machine. The pink-head took the paper, reading it over with a serious, hardened gaze; the expression on his face contorting into what could only be described as frustration.

"Corract again, Szayelaporro...but I don't think it's something to be happy about." He muttered to himself, placing the hand that held the results flat on his desk while the other was used to hold up his head. He adored being right; everyone in the city knew he prided himself in being so; but for once in his life, Szayel hated having such perfect knowledge of things.

_Especially now..._

The door to his laboratory opened, revealing the figure known as Sosuke Aizen. The ruler of Las Noches stood straight, his false smile plastered on his face as he stepped into the room. "You wanted to see me, Szayel?" He questioned the scientist, wondering what was so urgent that he had to be seen in privacy.

"Hai, Aizen-sama. It's about Ulquiorra." He informed the lord with so much reluctance. Saying this could very ruin the Cuatro, but it was only a matter of time before Aizen himself noticed the shift within his Cuatro.

A brow perked, the former shinigami captain asked: "What about him, Szayel?"

The scientist sighed, beginning to tell the lord about what he had found out after meeting with Ulquiorra that morning.

* * *

_The Octova Espada knocked once before entering the Cuatro House. Each Espada house was made to an approximate size, suiting towards the Espada's style. Ulquiorra, being the fourth highest in rank, had a very large accommodation; however, scarcely used it for any more than sleeping and eating in privacy. It was neat, of course, and extremely bleak, as the raven-haired arrancar never saw the need to decorate. In fact, it was bare of a lot of the basics one would expect in the large household. Not that he had room to complain; it was Ulquiorra's house, making it his choice on how to decorate. _

_No matter how much Szayel despised standing in it._

_Said Cuatro was waiting on the second to last step to the large staircase of the manor he was living in; awaiting as patiently as he could for the 'doctor' to show up. He was rather jittery, you could tell because his fingers refused to rest alongside the hands that held his arms. Intrigued, Szayel sat down beside him; getting out his tools as he greeted his superior. "Hello, Ulquiorra-san," he said in his usual cheerful tone._

_Green eyes shot into gold ones, revealing the iciest glare Szayel had ever seen Ulquiorra produce. The look itself made Szayel flinch; all muscles stiffening and eyes wide in fear that he had provoked his superior. "Get on with it," he ordered, calming down but only slightly. He wanted this dealt with and gone-**now!**_

_Szayel, wary of the ebony's mood, went to get out the basics. He started with the ear thermometer. "Tell me, Ulquiorra-san, what symptoms have you come across that you can tell me of?" He asked just as the device beeped; leaving the Cuatro to think as the pink-head checked the results._

_100.1_

_A low-grade fever, not much to worry about if Ulquiorra took it easy for the next few days. That is, unless the symptoms he reported prove it be otherwise. "I do not know how it started, but..." Ulquiorra paused, allowing Szayel to check his pupil dilation. "I've wrought a case of insomnia; I'm lucky to get half the sleep I'm used to getting." He began._

_Well, that certainly helped explain his mood. "Well, you do have a small fever," Szayel started, seeing that the information was a tad bit calming to the other. Ulquiorra was never one to want to remain bedridden, that was a fact. However, informing the latter was calming to Szayel, because Ulquiorra had an even larger concept of questioning things when they didn't make sense to him. Unless, of course, it came out of Aizen's mouth. "Is there any more than the insomnia?" He questioned._

_Ulquiorra reluctantly nodded once. "I've also been hallucinating through the day-I can't focus straight. It's gotten to the point where my patience is only tested further; as if every arrancar around me were somehow a threat. It's absurd!" He growled out, getting annoyed. Emotion was always something Ulquiorra never wanted the world to see; that was slowly being melted away, and it was getting to him even further.  
_

_Szayel caught this, making his eyebrow perk. "Every arrancar?" He asked, getting out a stethoscope so Ulquiorra would take some deep breaths and calm down. Not once had he seen the paler male so close to snapping; never to this point. It made the scientist grateful that Ulquiorra was in need of him right now, otherwise, he'd fear for his own safety._

_The Cuatro shook his head. "No, not truly; most of these come from males." He admitted, removing his jacket and taking in deep breaths as Szayel pressed the device against his chest._

_The pink head was caught off guard with this information. Normally, he wouldn't consider it much, as most arrancar felt this way whenever they were getting ill, or thought they were getting weaker. But this was Ulquiorra Cifer he was talking about. The man had never felt that way before; he knew who was a threat to him and who were not, and even if he didn't, it wasn't likely he'd ever voice it. _

_This made Szayel suspicious._

_"I see." He told his superior as he pressed the stethoscope against the latter's back. "Ulquiorra-san, this is me making an assumption, but...have you been soiling your covers, recently?" He questioned. The muscles in Ulquiorra's back stiffened and his breath was caught in his throat. What was he supposed to say to that?_

_Szayel removed the stethoscope and patiently awaited Ulquiorra's response; if he was right, like he always was, then any short snip would be enough for the ebony to take as an insult. That in mind, he remained silent in order to avoid getting killed in some form._

_After a few moments, the emerald-eyed male gave a curt nod before putting his coat back on. "Okay..." Szayel trailed off, gently taking the man's wrist to check his pulse before firing up another question. "And the reason for your early rising...wouldn't involve a form of dreaming, would it?" He questioned._

_Ulquiorra nodded again before hardening a glare Szayel's way. "How do you know about this?" He questioned the male, ready to kill him should he learn this was the cause of an experiment._

_This was expected, but Szayel was unfazed by it; it was a natural reaction, after all. "I know," he stated, "because this has happened before. Several other arrancar have come to me with similar symptoms and have rarely been diagnosed with something else." He informed the male, calmly._

_The gaze didn't soften to its neutrality; it was far from it. "Then what is wrong with me?" He practically yelled at the octova as he pounded his fist into the stairwell. His patience had long since run thin, and he wanted answers. More importantly, he wanted this gone as soon as possible.  
_

_Szayel shook his head. "I can't be positive until I've run a test, first. However, just to be sure of myself on my theory," he said standing up; equipment put away, " in these dreams...you wouldn't happen to be arousing someone by touching them, would you?" He asked the male. Hesitantly, Ulquiorra gave another reluctant nod. Szayel sighed. "All right, then," he said, getting out a vile and syringe. "Hold out your arm, Ulquiorra-san; I need to get a sample."_

* * *

Aizen sat before Szayel with a displeased expression. This had happened before, and it was easily dealt with because those others were immediately dealt with and not heard from again. But, he couldn't do such a thing to Ulquiorra; he was far too valuable of a tool. "The results?" He questioned, partially hoping that this was some form of infection or other condition.

Szayel shook his head. "I'm afraid Ulquiorra has reached the Profession stage of his life." He told his lord with much disdain. This issue never ended well for the patient.

This only displeased the brunette further. "Does he know about this, yet?" He asked Szayel.

The scientist shook his head. "I asked him to come down after lunch hour; I honestly don't know how I'm going to explain this to him, though." He admitted upfront. Hell, he wasn't sure if Ulquiorra would even understand everything.

The former captain of the fifth let out a sigh. This was troubling. "I'll be here for informing him, then." He stated, a neutral expression rising upon Aizen's features.

"Aizen-sama-"

"We'll need to prepare him for departure from Las Noches." And with that, the shinigami left his Octova; a frown tracing his lips.

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_**Like? Hate? Please be honest; I want this to be good!**_


	3. Welcome To Russia

**here's chapter three! hope u enjoy!**

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**Fireheart**

**Chapter Three**

_**Welcome To Russia**_

Ulquiorra was in a human apartment complex; a gigai stuck to his form in order to make him visible to humans. He had seen Szayel the day before to find out what the test results said only to be overloaded with detail that he wasn't ready to hear. What's worse was that his lord was informed before he was, and he found it excruciatingly embarrassing that Aizen had to see him in such a state.

Especially one that required him to leave Las Noches...

* * *

The Cuatro walked towards Szayel's lab at the appropriate time he was given, more than ready to treat this disease. It was irking him to no end and for his sanity, he needed this crazy ride to stop_-now!_

The ebony knocked once, waiting for a response. "Come in, Ulquiorra-san!" said the scientist's cheery voice; too much for the superior's liking.

Suppressing a growl, Ulquiorra entered the laboratory; expecting the Octova to tell him what the hell was going on with him before he broke him in two. What he didn't expect was to find a brunette shinigami in the room, as well...

He stopped in his tracks; eyes wide at the sight of his lord present. What was he doing here? He shot a glare towards Szayel as a means of asking the very question without having to voice such horrid emotion within his ruler's earshot. "Calm down, Ulquiorra," his lord commanded. Green eyes darted in the opposite direction; a puzzled look crossing his features. Aizen but only smiled. "I'm here to help Szayel explain your predicament, as most do not tend to fully understand."

His brow only rose in confusion. "You'll want to sit down, Ulquiorra-san; this is a rather...tedious topic and may take awhile to explain." Szayel instructed; giving the Cuatro a serious expression. Oh, he was _not_ looking forward to this conversation...

Ulquiorra complied silently; attention drawn to the two before him and awaiting the results of the blood test. "I was hoping to not have this talk with you, Ulquiorra-san," the scientist admitted, "but, as the test has it, there was no avoiding this."

"What do you mean?" Ulquiorra had demanded more than asked.

Szayel took a seat in front of the shorter male, a long sigh escaping his lips before he asked: "Did you know that hollows go through different stages in there lives?" The ebony shook his head. "Well, like humans, these stages show signs of maturity to our kind; however, like shinigami, these stages are prolonged and can come at any given time in their existence."

A brow arched only but slightly, Ulquiorra questioned: "Are you saying that this is my current position?" Szayel nodded promptly. "Then this is natural." He stated calmly. Again he received a nod from the pink-haired male. "Am I to assume that this stage you are speaking of is somewhat significant?"

"Regrettably...yes." The Cuatro's head turned towards his lord. The man was no longer smiling and instead giving him a calm, more serious expression; a sign that the former shinigami captain was not pleased with the situation. "Most stages do not, as they have no ulterior effect on the person in question; it's this stage that presents itself as a problem."

"Aizen-sama?" Ulquiorra questioned, not understanding what he meant.

There was a short pause before the brunette spoke again; his expression not faltering in the slightest. "The stage you are at," his lord began, "is what's called: The Profession Stage. This point in a hollow's life is what's considered to be the most efficient to come across; specifically because it affects behavior and personality just as much as it does growth." He stated.

The stoic Espada didn't know what to make of the explanation, and he made that obvious with an expectant gaze towards Szayel. Taking the hint, the latter continued: "Do you know what mating season is, Ulquiorra-san?"

"A time consisting of two to three months where hollows find a temporary partner in the attempt to reproduce." The Cuatro answered simply. "Why would such an unnecessary action concern my position?" He questioned.

Szayel let out a sigh; pinching the bridge of his nose. Well...at least Ulquiorra understood that much; it left a lot of explaining out of the loop that was just too awkward too talk about. "The Profession Stage, Ulquiorra-san, is rather similar to mating season only with a few differences in both behavior and the impact on the individual in question."

Ulquiorra, to say the least, was still trying to understand why this was such a big deal. If this was similar to mating season, then this should be able to be dealt with, soon. Besides, what's the worst it could do to him?

"Szayelapporro, go over these differences with Ulquiorra." Aizen ordered.

"Hai." Szayel sighed out before returning his attention to the superior Espada. "First off, mating season would effect most dominant arrancar, mostly male; the only exceptions I've found thus far are myself, you, and Harribel-san. They act on instinct to find the first submissive type that was unclaimed and make them their mate so they can reproduce." Ulquiorra nodded once, showing that he understood. "The Profession Stage effects all dominant arrancar at some point within their existence. The instinctual impulse is different, however."

Ulquiorra's brow rose, his back resting firmly against the chair provided. "And that means what, exactly?"

The scientist cleared his throat. "It means instead of claiming the first unmarked submissive you find, you will only claim a mate called a Chosen to by you. Dominant arrancar typically dream about having this Chosen by them in some form; mainly by arousing them. These dreams have a tendency to cause severe erections, as you've been waking up to lately." Well, that explained how Szayel knew what he had been dreaming about. "However, hollows won't claim this Chosen unless they submit by pure free will. The instinct, therefore, is to find this Chosen and to convince he or she to remain by the hollow's side. In this case, you."

"What for?" Ulquiorra questioned.

"Mating, Ulquiorra." The immediate response came from Aizen. "The biggest difference between mating season and the Profession Stage is that mating season allows hollows to mate temporarily in order to reproduce. The Profession Stage, though, is an instinct provided by the soul to go in search for a permanent partner, and seek their companionship for more emotional purposes rather than the instinct of reproduction."

To say that the Cuatro was pleased with the explanation was so far from the truth, it wasn't funny. Ulquiorra's eyes now resembled dinner plates, as he was caught off guard. Emotional purposes? What emotion? Ulquiorra didn't have any, he was thoroughly hollow; they did not feel for others, their only real instinct was to survive.

With a sigh, his lord continued. "The instinct to find and claim this other isn't all. In this case we're speaking of you, but the hollow's persona will deliberately change for the sake of their Chosen accepting their offer, and their protective instincts will make him wary of all dominant arrancar. These instincts cause your insomnia and short-temper, Ulquiorra." The brunette explained.

Ulquiorra took in a deep breath, a hand placed on his forehead as he attempted to process all of the information. It was quiet for a good while; the two standing not saying a word in order to let Ulquiorra come to term on the matter. After a what felt like hours, the Cuatro spoke again. "And there is no stopping this?" He questioned them, not liking where this was going.

"Unfortunately, no." Aizen replied. "We've tried numerous tactics, however the Profession Stage is a natural course in a hollow's life and can't be restrained. Such tactics lead to disastrous results. So, we've settled for different matters in order to determine what to do with these individuals; we test their loyalty to Las Noches. If they fail, they are either destroyed or banished. If they succeed, they are allowed to go out in search of this other and return with them. The latter has yet to occur, though."

"Then I too must prove my loyalty." Ulquiorra concluded.

Aizen chuckled a bit as he approached the ebony. "There's no need, Ulquiorra; you are already my most loyal servant. I know you wouldn't dare try to betray me." The male stated.

Ulquiorra had to force himself to not seem desperate. "What is it that I'm supposed to do about this, then, Aizen-sama?" The Cuatro questioned, honestly still trying to regain his composure.

"I do believe I've already told you, Ulquiorra," he replied smoothly, placing a hand on the Espada's shoulder. "You are going to go in search of your Chosen, and bring he or she back here so you can be together." And with that, the ruler left the room to allow his servant to think.

After sitting there for a few more minutes, the Cuatro left in order to go prepare for his departure.

* * *

The ebony arrancar was now in St. Petersburg, Russia, and to say the least, it was freezing outside. Of all the places to end up, he landed in an ice desert. He was thankful for the generous amount of heat the accommodations provided, but wasn't going to be there long. Before leaving, Szayel told him to follow his instincts and he'd find his Chosen faster. Right now, he had hated them for getting him into such a cold country, and said instincts currently felt like he should be walking around outside.

As much as he hated the cold, he wanted to get the assignment over with and done. So, getting on a few layers of clothing before putting on the winter gear provided, Ulquiorra headed out onto the streets and began walking in the first direction his mind thought up, muttering: "Welcome to Russia..."

* * *

**Well, I'm glad that that's done! Sorry about the long wait, but the lack of reviews is rather depressing -_-. Therefore, I refuse to update until such time I get at least ten reviews. I hope you've enjoyed.**

_**~ K. Fang-sama**_


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